U.S. patent application number 10/784953 was filed with the patent office on 2004-09-09 for sheet processsing apparatus and image forming apparatus having such sheet processing apparatus.
This patent application is currently assigned to Canon Fintech Inc.. Invention is credited to Kato, Hitoshi, Obuchi, Yusuke, Suzuki, Hiroshi, Terada, Tetsuya.
Application Number | 20040175216 10/784953 |
Document ID | / |
Family ID | 32923665 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040175216 |
Kind Code |
A1 |
Obuchi, Yusuke ; et
al. |
September 9, 2004 |
Sheet processsing apparatus and image forming apparatus having such
sheet processing apparatus
Abstract
A pressing member is provided on a shutter member provided in a
main body of an apparatus and adapted to open and close a folded
sheet discharging port upon upward and downward shifting movement
of sheet stacking means in such a manner that, after folding
processing is performed by folding means as the shutter member is
lowered, a sheet discharged onto folded sheet stacking means is
pressed down by the pressing member. Further, if there is any sheet
on the folded sheet stacking means, by stopping the sheet stacking
means at a predetermined position where the shutter member lightly
abuts against the sheet discharged on the folded sheet stacking
means, the sheet is prevented from being pinched between the
shutter member and the sheet stacking means.
Inventors: |
Obuchi, Yusuke; (Chiba,
JP) ; Kato, Hitoshi; (Ibaraki, JP) ; Suzuki,
Hiroshi; (Ibaraki, JP) ; Terada, Tetsuya;
(Ibaraki, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Fintech Inc.
Ibaraki-ken
JP
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
32923665 |
Appl. No.: |
10/784953 |
Filed: |
February 25, 2004 |
Current U.S.
Class: |
399/407 |
Current CPC
Class: |
G03G 2215/00877
20130101; G03G 15/6573 20130101 |
Class at
Publication: |
399/407 |
International
Class: |
G03G 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2003 |
JP |
2003-062542 |
Claims
What is claimed is:
1. A sheet processing apparatus having folding means for folding a
sheet on which an image was formed and wherein the sheet folded by
said folding means is discharged onto a folded sheet stacking
portion through a folded sheet discharging port, comprising: sheet
stacking means provided in a main body of said apparatus for a
shifting movement in an up-and-down direction and adapted to stack
a sheet discharged from an upper discharging port provided above
said folded sheet discharging port without passed through said
folding means; a shutter member provided in said main body of said
apparatus for a shifting movement in an up-and-down direction and
adapted to be lifted and lowered upon upward and downward shifting
movements of said sheet stacking means to open and close said
folded sheet discharging port; and a pressing member provided on
said shutter member and adapted to push the sheet stacked on said
folded sheet stacking portion.
2. A sheet processing apparatus according to claim 1, further
comprising position control means for stopping said sheet stacking
means at a predetermined position where said shutter member lightly
abuts against the sheet stacked on said folded sheet stacking
portion when said sheet stacking means are lowered in a condition
that the sheet is stacked on said folded sheet stacking
portion.
3. A sheet processing apparatus according to claim 2, wherein said
position control means include folded sheet detecting means for
detecting the sheet stacked on said folded sheet stacking portion
and position detecting means for detecting the fact that said sheet
stacking means reach the predetermined position where said shutter
member lightly abuts against the sheet stacked on said folded sheet
stacking portion.
4. A sheet processing apparatus according to claim 3, wherein said
position detecting means are provided at a position where said
position detecting means detect said sheet stacking means reached
to the predetermined position where said shutter member lightly
abuts against the sheet stacked on said folded sheet stacking
portion.
5. A sheet processing apparatus according to claim 3, wherein said
position detecting means are designed so that said position
detecting means detect the fact that said sheet stacking means
reach the predetermined position where said shutter member lightly
abuts against the sheet stacked on said folded sheet stacking
portion, on the basis of a sheet stacking height of the sheet
stacked on said sheet stacking means.
6. A sheet processing apparatus according to claim 5, wherein said
position detecting means detect the fact that the sheet stacked on
said sheet stacking means reaches a predetermined sheet stacking
height, by detecting a position of an uppermost sheet among sheets
stacked on said sheet stacking means.
7. A sheet processing apparatus according to claim 5, wherein said
position detecting means the sheet stacking height of sheets
stacked on said sheet stacking means by counting the number of
sheets discharged onto said sheet stacking means.
8. An image forming apparatus comprising: an image forming portion
for forming an image on a sheet; and a sheet processing apparatus
according to any one of claims 1 to 7, for processing the sheet on
which the image was formed by the image forming portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sheet processing
apparatus having folding means for folding a sheet on which an
image was formed, and an image forming apparatus having such a
sheet processing apparatus. More specifically, the present
invention relates to a sheet processing apparatus which can be made
compact and can prevent damage of a sheet, and an image forming
apparatus having such a sheet processing apparatus.
[0003] 2. Related Background Art
[0004] Conventionally, regarding image forming apparatuses such as
copiers, printing machines, laser beam printers and the like, there
has been proposed a sheet processing apparatus in which, for
example, after sheets on which images were formed and discharged
from a main body of the image forming apparatus are successively
received, the sheets are conveyed to folding means, where
double-folding processing is carried out, and, thereafter, the
sheets are discharged onto a sheet stacking portion (refer to
Japanese Patent Application Laid-open No. 2001-26359).
[0005] FIG. 5 is a schematic constructional view of a conventional
sheet processing apparatus having such a construction. As shown in
FIG. 5, a sheet processing apparatus 1000 includes conveying
rollers 203, a sheet stopper 205, a stapler 206, a thrusting plate
(folding means) 209, a pair of folding rollers 208, sheet
discharging rollers 210 and a stacking tray (sheet stack stacking
means) 211, in order to perform such folding processing.
[0006] Here, in the sheet processing apparatus 1000, a sheet
discharged from a main body of an image forming apparatus (not
shown) and conveyed into the sheet processing apparatus is firstly
conveyed by the conveying rollers 203 until a leading end of the
sheet reaches the sheet stopper 205, and, thereafter, lateral sides
of the sheet reached to the sheet stopper 205 are aligned by sheet
aligning means (not shown).
[0007] By repeating such operations with respect to a plurality of
sheets, the plurality of sheets are stacked on the sheet stopper
205 and, then, stapling processing is performed by the stapler-206.
Thereafter, by thrusting the thrusting plate 209 toward a central
portion of the stacked sheets, the sheet stack is advanced into a
nip of the folding roller pair 208, so that the sheet stack is
double-folded by the folding roller pair 208. Thereafter, the
double-folded sheet stack is discharged by the sheet discharging
rollers 210 onto the stacking tray 211 through a stack discharging
outlet 611 provided at a lower part of a main body 1001 of the
sheet processing apparatus.
[0008] By the way, in a case where the sheet stack so double-folded
is discharged onto the stacking tray 211, since the sheet stack is
swollen upwardly in a folded portion at a discharging side end, if
a plurality of sheet stacks are stacked on the stacking tray 211, a
discharging downstream side of the sheet stacked on the stacking
tray 211 will be swollen upwardly.
[0009] If the discharging sides of the sheet stacks are swollen in
this way, since subsequent discharging of the sheet stack onto the
stacking tray cannot be performed properly, as shown in FIG. 5, a
pressing member 212 for pressing the discharging downstream sides
of the sheet stacks is provided above the stacking tray 211 for a
rotational movement around a fulcrum 216.
[0010] On the other hand, in FIG. 5, there are also provided a
sample tray 701 on which sheets passed through a non-sort path 521
after conveyed from the main body of the image forming apparatus
(not shown) are stacked, and a stack tray 700 on which sheets after
passed through a sort path 522 and subjected to aligning
processing, if necessary, and stapling processing effected by a
stapler 601 are discharged.
[0011] By the way, the stack tray 700 can be moved in an
up-and-down direction so that, as a sheet stacking amount is
increased, the stack tray is shifted downwardly. When the stack
tray 700 is shifted downwardly to pass by the stack discharging
outlet 611, the sheets stacked on the stack tray 700 may enter into
the stack discharging outlet 611.
[0012] To avoid this, in the past, the main body 1001 of the sheet
processing apparatus is provided with a shutter member 613 for
opening and closing the stack discharging outlet 611 so that, when
the stack tray 700 is lowered, by lowering the shutter member 613
together with the stack tray 700, the stack discharging outlet 611
is closed. By closing the stack discharging outlet 611 upon
lowering of the stack tray 700, the sheets stacked on the stack
tray 700 are prevented from entering into the stack discharging
outlet 611.
[0013] Incidentally, the shutter member 613 is biased upwardly by
an extension spring 615 so that the shutter member 613 is normally
held at a position for opening the stack discharging outlet 611
and, when the stack tray 700 is lifted, the shutter member is
lifted by following the stack tray 700, thereby opening the stack
discharging outlet 611.
[0014] However, in the conventional sheet processing apparatus
having the above-mentioned shutter member 613 and pressing member
212 and an image forming apparatus having such a sheet processing
apparatus, in a case where the pressing member 212 is protruded
from the stack discharging outlet 611 out of the main body 1001 of
the sheet processing apparatus, since the pressing member 212
constitutes an obstruction, the shutter member 613 cannot be
lowered adequately. To avoid this, as shown in FIG. 5, the pressing
member 212 is provided within the main body 1001 of the sheet
processing apparatus.
[0015] However, in a case where the pressing member 212 is provided
within the main body 1001 of the sheet processing apparatus in this
way, a lateral dimension of the main body 1001 of the sheet
processing apparatus is increased, which makes the sheet processing
apparatus 1000 bulky, with the result that the image forming
apparatus having the sheet processing apparatus 1000 is also made
bulky. Further, in the case where the pressing member 212 is
disposed within the apparatus, the sheet stacks to be discharged
and stacked also remain within the apparatus, which causes a
problem that it is difficult to take out the sheet stack.
[0016] On the other hand, in the case where the pressing member 212
is provided within the main body 1001 of the sheet processing
apparatus, although the shutter member 613 can be lowered
adequately, if the shutter member 613 is lowered too great, the
sheet stack may be pinched between the shutter member and the
stacking tray 211. If the sheet stack is so pinched, the sheet
stack may be damaged.
SUMMARY OF THE INVENTION
[0017] The present invention is made in consideration of the
above-mentioned circumstances, and an object of the present
invention is to provide a sheet processing apparatus which can be
made compact and can prevent damage of a sheet, and an image
forming apparatus having such a sheet processing apparatus.
[0018] To achieve the above object, the present invention provides
a sheet processing apparatus having folding means for folding a
sheet on which an image was formed and in which the sheet folded by
the folding means is discharged onto a folded sheet stacking
portion through a folded sheet discharging port, comprising sheet
stacking means provided in a main body of the apparatus for a
shifting movement in an up-and-down direction and adapted to stack
a sheet discharged from an upper discharging port provided above
the folded sheet discharging port without passed through the
folding means, a shutter member provided in a main body of the
apparatus for a shifting movement in an up-and-down direction and
adapted to be lifted and lowered upon upward and downward shifting
movements of the sheet stacking means to open and close the folded
sheet discharging port, and a pressing member provided on the
shutter member and adapted to push the sheet stacked on the folded
sheet stacking portion.
[0019] Further, in the present invention, there is further provided
position control means for stopping the sheet stacking means at a
predetermined position where the shutter member lightly abuts
against the sheet stacked on the folded sheet stacking portion when
the sheet stacking means are lowered in a condition that the sheet
is stacked on the folded sheet stacking portion.
[0020] Further, in the present invention, the position control
means include folded sheet detecting means for detecting the sheet
stacked on the folded sheet stacking portion and position detecting
means for detecting the fact that the sheet stacking means reach
the predetermined position where the shutter member lightly abuts
against the sheet stacked on the folded sheet stacking portion.
[0021] Further, in the present invention, position detecting means
are provided at a position where the position detecting means
detect the sheet stacking means reached the predetermined position
where the shutter member lightly abuts against the sheet stacked on
the folded sheet stacking portion.
[0022] Further, in the present invention, the position detecting
means are designed so that the position detecting means detect the
fact that the sheet stacking means reach the predetermined position
where the shutter member lightly abuts against the sheet stacked on
the folded sheet stacking portion, on the basis of a sheet stacking
height of the sheet stacked on the sheet stacking means.
[0023] Further, the present invention provides an image forming
apparatus comprising an image forming portion for forming an image
on a sheet, and one of sheet processing apparatuses as mentioned
above.
[0024] As mentioned above, as is in the present invention, by
providing, on the shutter member, the pressing member for pushing
the sheet discharged on the folded sheet stacking portion, the
apparatus can be made compact, and a large number of sheets can be
stacked by lowering the shutter member and the pressing member by
means of the stack tray when there is no sheet on the folded sheet
stacking portion. Further, in a case where there is any sheet on
the folded sheet stacking portion, by stopping the sheet stacking
means at a position where the shutter member does not abut against
the sheet discharged on the folded sheet stacking portion, the
sheet can be prevented from being pinched between the shutter
member and the folded sheet stacking portion, thereby preventing
damage of the sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a view showing a schematic construction of a
copier as an example of an image forming apparatus having a sheet
processing apparatus according to a first embodiment of the present
invention;
[0026] FIG. 2 is a schematic constructional view of the sheet
processing apparatus;
[0027] FIG. 3 is a view showing a condition that a pressing member
is rotated upwardly when a shutter member is lowered together with
a stack tray provided in the sheet processing apparatus;
[0028] FIG. 4 is a schematic constructional view of a sheet
processing apparatus according to a second embodiment of the
present invention; and
[0029] FIG. 5 is a view showing a schematic construction of a
conventional sheet processing apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Now, embodiments of the present invention will be fully
explained with reference to the accompanying drawings.
[0031] FIG. 1 is a view showing a schematic construction of a
copier as an example of an image forming apparatus having a sheet
processing apparatus according to a first embodiment of the present
invention.
[0032] In FIG. 1, a copier 100 is constituted by a main body 101 of
an apparatus and a finisher 119 as a sheet processing apparatus. A
document or original feeding apparatus 102 is provided on an upper
part of the main body 101 of the apparatus. Documents D are stacked
on a document stacking portion 103 by an operator and are separated
and fed one by one by means of a feeding portion 104 to a pair of
registration rollers 105. Then, the document D is temporarily
stopped by the registration roller pair 105 so that a loop is
formed in the document to correct skew-feeding. Thereafter, the
document D is passed through an introduction path 106 and then is
passed through a reading position 108 where an image formed on a
surface of the document is read. The document D passed through the
reading position 108 is passed through a discharging path 107 and
then is discharged onto a discharging tray 109.
[0033] Further, in a case where both surfaces of the document are
read, first of all, an image on one surface of the document is read
by passing the document through the reading position 108 as
mentioned above. Thereafter, the document D is passed through the
discharging path 107 and then is switchback-conveyed by a pair of
turn over rollers 110, so that the document is conveyed to the
registration roller pair 105 again in a condition that a front
surface of the document is reversed to a rear surface thereof.
[0034] Then, similar to the reading of one surface of the document,
the skew-feeding of the document D is corrected by the registration
roller pair 105 and then the document is passed through the
introduction path 106 to reach the reading position 108 where an
image on the other surface is read. Then, the document D is passed
through the discharging path 107 and is discharged onto the
discharging tray 109.
[0035] On the other hand, the document passing through the reading
position 108 is illuminated by light from an illumination system
111, and, thereafter, reflection light reflected from the document
is directed to an optical element (CCD or other element) 113 by
means of a mirror 112, where the light is converted into image
data. Then, by illuminating a laser beam onto a photosensitive drum
114 on the basis of the image data, a latent image is formed on the
photosensitive drum. Further, thereafter, the latent image formed
on the photosensitive drum 114 is developed by toner supplied from
a toner supplying apparatus (not shown), thereby forming a toner
image on the photosensitive drum 114.
[0036] Further, in synchronous with the formation of the toner
image, a sheet such as a paper or a plastic film situated in a
cassette 115 is fed out from the cassette 115 in response to a
recording signal and is sent between the photosensitive drum 114
and a transferring device 116. Then, the toner image on the
photosensitive drum 114 is transferred onto the sheet by the
transferring device 116, and, thereafter, the sheet to which the
toner image was transferred is sent to a fixing apparatus 117,
where the toner image is fixed to the sheet by heat and
pressure.
[0037] Incidentally, in a case where images are formed on both
surfaces of the sheet, the sheet to which the image was fixed onto
one surface of the sheet by the fixing apparatus 117 is passed
through a both-face path 118 provided at a downstream side of the
fixing apparatus 117 and then is sent between the photosensitive
drum 114 and the transferring device 116 of an image forming
portion again, where a toner image is also transferred onto a rear
surface of the sheet. Then, the toner image is fixed onto the rear
surface, and the sheet is discharged outside (toward the finisher
119).
[0038] On the other hand, the finisher 119 successively receives
the sheets discharged from the main body 101 of the apparatus and
performs various processing operations such as processing for
aligning the received plural sheets and for bundling the sheets as
a single stack, stapling processing for stapling the bundled sheet
stack, sorting processing, non-sorting processing and book binding
processing. As shown in FIG. 2, the finisher includes a folding
apparatus 400, a processing portion 500 and the like.
[0039] As shown in FIG. 2, the processing portion 500 includes a
pair of inlet rollers 502 for directing the sheet conveyed from the
main body 101 (FIG. 1) of the apparatus toward inside, and a
flapper 551 for directing the sheet to a non-sort path 552 in a
non-sort mode and a sort mode and to a book binding path 553 in a
folding mode.
[0040] In case of the non-sort mode, the sheet directed into the
non-sort path 552 by the flapper 551 is discharged onto the sample
tray 701 of a normal rotation of a pair of reversible sheet
discharge conveying rollers 509.
[0041] Further, in case of the sort mode, the sheet directed into
the sort path 552 by the flapper 551 is stacked onto an
intermediate tray (referred to as "processing tray" hereinafter)
630 by a reverse rotation after a predetermined amount normal
rotation of the pair of sheet discharge conveying rollers 509.
Incidentally, the sheets stacked on the intermediate tray as a
bundle are subjected to aligning processing if necessary and
stapling processing effected by a stapler 601 and then are
discharged onto a stack tray 700 as sheet stacking means designed
to be shifted in an up-and-down direction, by means of the pair of
sheet discharge conveying rollers 509.
[0042] On the other hand, the folding apparatus 400 includes two
pairs of staplers 818, and a pair of folding rollers 826 as folding
means for folding the sheet. The sheet sent from the book binding
path 553 is housed in a housing guide 820 by a pair of conveying
rollers 813 and, thereafter, the sheet is conveyed until a leading
end of the sheet is contacted with a positioning member 823 which
is shiftable in an up-and-down direction.
[0043] Here, there is a provided a thrusting member 825 as
thrusting means in a confronting relationship to the pair of the
folding rollers 826 with the interposition of the housing guide
820. By thrusting the thrusting member 825 opposed to the pair of
folding rollers 826 toward the sheet stack housed in the housing
guide 820, the sheet stack is pushed out into a nip portion as a
folding portion of the folding roller pair 826 to be folded by the
folding roller pair 826. Thereafter, the folded sheet stack is
discharged onto a saddle discharging tray 832 as a folded sheet
stacking portion by a pair folded sheet discharging rollers
827.
[0044] Incidentally, in a case where the sheet stack stapled by the
stapler 818 is folded, after the stapling processing is finished,
the positioning member 823 is lowered by a predetermined distance
so that a stapled position of the sheet stack is situated at a
central portion of the folded roller pair 826.
[0045] By the way, in FIG. 2, there are also provided a stack
discharging port as a folded sheet discharging port 833 for
discharging the sheet stack subjected to the folding processing
onto the saddle discharging tray 832, and a shutter member 702
provided on a main body 119A of the finisher for a shifting
movement in an up-and-down direction and adapted to open and close
the stack discharging port 833, and the shutter member 702 can be
lowered as the stack tray 700 is lowered.
[0046] Incidentally, the shutter member 702 is biased upwardly by
an extension spring 703 so that the shutter member 702 is normally
held at a position for opening the stack discharging port 833 and,
when the stack tray 700 is lifted, shutter member 702 follows the
stack tray 700 to be lifted, thereby opening the stack discharging
port 833.
[0047] Further, there is also provided a pressing member 850
disposed above the saddle discharging tray 832 and adapted to push
down a discharge side of the sheet stack. By pressing down the
discharge side of the sheet stack by means of the pressing member
850, a subsequent sheet stack can be discharged onto the saddle
discharging tray properly.
[0048] The pressing member 850 is attached to a lower end portion
of the shutter member 702. By providing the pressing member 850 at
the lower end portion of the shutter member 702 in this way, a
width-wise direction of the main body 119A of the finisher can be
reduced in comparison with a case where the pushing member is
provided within the main body of the finisher (refer to FIG. 5),
thereby making the finisher 119 and therefore the copier 100 (FIG.
1) having the finisher 119 compact.
[0049] Incidentally, in the illustrated embodiment, one end 850a of
the pressing member 850 is rotatably supported at the lower end
portion of the shutter member 702 so that, after the pressing
member 850 abuts against the sheet stack as shown in FIG. 3, when
stack tray 700 is lowered and the shutter member 702 is lowered
accordingly, the pressing member 850 is rotated upwardly.
[0050] By rotating the pressing member 850 upwardly after it abuts
against the sheet stack in this way, the stack tray 700 and the
shutter member 702 can be lowered without obstructed by the
pressing member 850. Incidentally, the pressing member 850 is held
in a condition shown in FIG. 2 by a locking member (not shown)
until it abuts against the sheet stack.
[0051] On the other hand, in FIG. 2, there are also provided a
sheet stacking detecting sensor S1 as folded sheet detecting means
provided on the saddle discharging tray 832 and adapted to detect
the sheet stack discharged onto the saddle discharging tray 832,
and a lower limit sensor S2 as position detecting means for
detecting the fact that the stack tray 700 reaches a predetermined
position (referred to as "lower limit position" hereinafter) where
the shutter member 702 lightly abuts against the sheet discharged
on the saddle discharging tray 832.
[0052] Detection signals from the sheet stack detecting sensor S1
and the lower limit sensor S2 are inputted into a control portion
860 provided in the main body 119A of the finisher (or the main
body 101 of the apparatus. The control portion 860 causes the
sheets discharged from an upper discharging port 834 provided above
the stack discharging port 833 and not folded to be stacked on the
stack tray 700 successively, and when the detection signal is
inputted from the lower limit sensor S2 detecting the stack tray
gradually lowered accordingly and reached the lower limit position,
the control portion checks presence/absence from the sheet stack
detecting sensor S1.
[0053] When the detection signal from the lower limit sensor S2 is
inputted in this way, if the detection signal from the sheet stack
detecting sensor S1 is inputted, i.e. if there is the sheet stack
on the saddle discharging tray 832, a motor (not shown) for lifting
and lowering the stack tray is stopped.
[0054] By providing the position control means constituted by the
sheet stack detecting sensor S1, lower limit sensor S2 and control
portion 860, if there is the sheet stack on the saddle discharging
tray 832, by stopping the stack tray 700 at the lower limit
position, the sheet stack can be prevented from being pinched
between the shutter member 702 and the saddle discharging tray 832,
thereby preventing the damage of the sheet stack.
[0055] By the way, in the above-mentioned explanation, while an
example that the stack tray 700 reaching the lower limit position
is directly detected by providing the lower limit sensor at the
lower limit position of the shutter member 702 was explained, the
present invention is not limited to such a example, but, for
example, the fact that the stack tray 700 reaches the lower limit
position may be detected on the basis of a sheet stacking height on
the stack tray 700.
[0056] FIG. 4 is a view showing a schematic construction of the
sheet processing apparatus according to a second embodiment of the
present invention. Incidentally, in FIG. 4, elements same as or
similar to those in FIG. 2 are designated by the same reference
numerals.
[0057] In FIG. 4, a stacking height detecting sensor S3 serves to
detect a stacking height of sheets stacked on the stack tray 700,
and the stacking height detecting sensor S3 constitutes a part of
the position control means for stopping the stack tray 700 at the
lower limit position together with the above-mentioned sheet stack
detecting sensor S1.
[0058] The stacking height detecting sensor S3 as position
detecting means constituting the position control means together
with the sheet stack detecting sensor S1 is turned ON by a flag 704
urged by an end of the sheet stack stacked on the stack tray 700
when the stack tray 700 is lowered, and output from the stacking
height detecting sensor S3 is inputted to the control portion
860.
[0059] When the stack tray 700 is lowered, the stacking height
detecting sensor S3 continues to be turned ON till an uppermost end
of the sheet stack stacked on the stack tray 700; that is to say,
an ON time of the stacking height detecting sensor S3 is lengthened
in accordance with the height of the sheet stack stacked on the
stack tray 700. The control portion 860 serves to detect the sheet
stacking height on the basis of the ON time of the stacking height
detecting sensor S3.
[0060] Since the position of the stack tray 700 can be detected by
detecting the sheet stacking height, when the ON time of the
stacking height detecting sensor S3 reaches a predetermined time,
i.e. when the sheet stacking height reaches a predetermined value,
the stack tray 700 can detect the fact that the shutter member 702
reaches the lower limit position.
[0061] Incidentally, in the illustrated embodiment, while an
example that the lower position of the stack tray 700 is detected
by directly detecting the sheet stacking height was explained, so
long as a thickness of the sheet is known, the sheet stacking
height may not be detected directly, but, the fact that the stack
tray 700 reaches the lower limit position may be detected by
counting the number of sheets discharged onto the stack tray
700.
* * * * *